Monitoring and analysis of seismic data during the 2018 sunda strait tsunami

The tsunami of Sunda Strait occurred on December 22, 2018, at 21:03 West Indonesia Time (zone). An eruption of Mount Anak Krakatau caused an eruption that triggered a landslide on the slopes of Mount Anak Krakatau covering an area of 64 hectares that hit the coastal area of western Banten and southern Lampung and resulted in 437 deaths, 14.059 people were injured, and 33.721 people were displaced. Before the tsunami, signal transmissions (gaps) at the Lava seismograph station installed on the body of Mount Anak Krakatau experienced broken so that Mount Anak Krakatau Observation Post could not record volcanic earthquake signals since December 22, 2018, at 21.03 West Indonesia Time (zone). Given these facts, proper monitoring and analysis were required to monitor and analyze the source of ground vibrations originating from the eruption of Mount Anak Krakatau. Therefore, this study aims to confirm the eruptive activity of Mount Anak Krakatau based on seismic monitoring and analysis sourced from the BMKG's seismic sensor network. The method the author uses is by monitoring the seismic signal recorded by the seismometer and analyzing the seismic signal using the Seiscomp3 software. By the results of monitoring and analysis of seismic data, it was found that the location of the center of the ground shaking was on Mount Anak Krakatau with a magnitude of 3.4, and a depth of 1 km. To anticipate similar tsunami events in the future, it is very necessary to have a tsunami early warning system originating from volcanic activity and volcanic body avalanches.

Origin Time of the 1854 Ansei–Tokai Tsunami Estimated from Tide Gauge Records on the West Coast of North America

We estimated the origin time of the 1854 Ansei–Tokai tsunami from the tsunami waveforms recorded at three tide gauge stations (Astoria, San Francisco, and San Diego) on the west coast of North America. The tsunami signal is apparent in the San Francisco and San Diego records, and the arrival time was 0–1 p.m. Greenwich Mean Time (GMT) on 23 December 1854, whereas the tsunami signal of Astoria is ambiguous, and the arrival time could not be determined from the waveform. The simulated waveforms on the basis of nonlinear dispersive wave theory by assuming an origin time of 0 a.m. GMT on 23 December arrived earlier than the observations. Cross-correlation functions between the observed and simulated waveforms recorded at San Francisco and San Diego showed a time gap between them of approximately 30 min. Based on these results, we concluded that the origin time of the 1854 Ansei–Tokai tsunami was approximately 00:30 a.m. GMT or 09:46 local time on 23 December. Our result is roughly consistent with reports by a Russian frigate anchored in Shimoda Bay, ranging the earthquake between 09:00 and 09:45 and the tsunami between 09:30 and 10:00. The earthquake was also reported in historical Japanese documents ranging from 8 and 10 o’clock in local time.

Identifying Criteria for Designing Risk Communication System in Palu, Sulawesi, Indonesia

The 2018 Sulawesi earthquake and tsunami in Indonesia signaled the failure of a risk communication system, causing Indonesia to be accused of mishandling the natural disaster. Many criticisms focused on allegations that the country’s meteorology and geophysics agency canceled the tsunami alert too early and misinformed public, that the sirens weren’t operable to warn local people, the tidal buoys did not work to send the tsunami signal, consequently, causing casualties. Improving the risk communication system raises the following question: what are the criteria for designing a risk communication system for areas in the disaster-prone zone? This paper employs multi-criteria decision analysis (MCDA) as a framework that is integrated with the combination of technical and cultural risk communication to provide such an answer. As for the findings, this study includes sixteen indicators that are distributed among nine criteria of a risk communication system within two types of measurement: qualitative and quantitative. It suggests that a risk communication system shall work better on a two-way process. Stakeholders’ and decision-makers’ involvement and public participation are required to make better decisions because it leads to better awareness of risks and greater acceptance of risk management strategies that are jointly agreed upon.

An Experimental Study of Surface Buoy Profiles to Improve the Accuracy of Seafloor Crustal Deformation and Tsunami Signal Observations of the On-Demand Buoy System

A hydraulic experiment was carried out to determine the optimal profile of surface buoys of the on-demand buoy system for observing seafloor crustal deformation and tsunami signals. The experiment used a rectangular flume with surface buoy models, and the surface buoy profile was changed by analogy with the profile of a tree crown that has been deformed by a stream. Then, the fluid force acting on the surface buoy was measured with a force transducer, and its drag coefficient was evaluated. The results showed that, for observation accuracy, a buoyancy unit with a 2D droplet profile and a lower structure with a 3D droplet profile were optimal.

Tsunami arrival time detection system applicable to discontinuous time series data with outliers

Timely detection of tsunamis with water level records is a critical but logistically challenging task because of outliers and gaps. Since tsunami detection algorithms require several hours of past data, outliers could cause false alarms, and gaps can stop the tsunami detection algorithm even after the recording is restarted. In order to avoid such false alarms and time delays, we propose the Tsunami Arrival time Detection System (TADS), which can be applied to discontinuous time series data with outliers. TADS consists of three algorithms, outlier removal, gap filling, and tsunami detection, which are designed to update whenever new data are acquired. After calibrating the thresholds and parameters for the Ulleung-do surge gauge located in the East Sea (Sea of Japan), Korea, the performance of TADS was discussed based on a 1-year dataset with historical tsunamis and synthetic tsunamis. The results show that the overall performance of TADS is effective in detecting a tsunami signal superimposed on both outliers and gaps.

Tsunami arrival time detection system applicable to discontinuous time-series data with outliers

Timely detection of tsunamis with water-level records is a critical but logistically challenging task because of outliers and gaps. We propose a tsunami arrival time detection system (TADS) that can be applied to discontinuous time-series data with outliers. TADS consists of three major algorithms that are designed to update at every new data acquisition: outlier detection, gap-filling, and tsunami detection. To detect a tsunami from a record containing outliers and gaps, we propose the concept of the event period. In this study, we applied this concept in our test of the TADS at the Ulleung-do surge gauge located in the East Sea. We calibrated the thresholds to identify tsunami arrivals based on the 2011 Tohoku tsunami, and the results show that the overall performance of TADS is effective at detecting a small tsunami signal superimposed on both an outlier and gap.

STATISTICAL AND SPECTRAL CHARACTERISTICS OF THE 2011 EAST JAPAN TSUNAMI SIGNAL IN ARRAIAL DO CABO, RJ, BRAZIL

ABSTRACT. For the second time, the sign of a tsunami could be measured in Brazil. The waves generated by the Mw 9.0 earthquake in Japan on March 11, 2011,have spread across the Pacific Ocean and through Drake Passage reached the Atlantic Ocean, being recorded by at least three tide gauges. During the 2004 Sumatraevent, the positioning of the tsunami source allowed the waves to propagate almost directly to the South American coast and the signal was recorded at many sites ofthe Argentinian, Uruguayan and Brazilian coast. This time, the path of the waves was much more complex, causing strong signal attenuation and making difficult thedetection of the waves. Nevertheless, the tsunami signal was identified at Arraial do Cabo, RJ, mainly due to the low background noise level. This far-field record wasused to estimate statistical and spectral characteristics of arriving tsunami waves.Keywords: Japan tsunami, signal detection, Brazil. RESUMO. Pela segunda vez, o sinal de um tsunami pôde ser registrado no Brasil. As ondas originadas pelo terremoto de magnitude 9,0 ocorrido no Japão, em 11 de março de 2011, se propagaram através do oceano Pacífico e, passando pelo Estreito de Drake, atingiram o oceano Atlântico, sendo registradas por, pelo menos, três marégrafos. No evento de 2004, a posição da fonte do tsunami permitiu a propagação quase direta das ondas até a costa sul americana e o sinal pôde ser registrado emdiversos pontos na Argentina, Uruguai e Brasil. Dessa vez, o caminho das oscilações foi bem mais complexo, provocando forte atenuação do sinal e, assim, dificultandosua detecção. Apesar disso, foi possível detectar esse sinal em Arraial do Cabo, RJ, principalmente devido ao baixo nível de ruído de fundo no registro do nível do mar. O registro desses dados de campo distante foi utilizado para extrair características estatísticas e espectrais dos dados coletados.Palavras-chave: tsunami do Japão, detecção do sinal, Brasil.

Review of Recent Tsunami Observation by Offshore Cabled Observatory

This paper discusses near- and far-field tsunami observations at the Hokkaido, Japan, offshore cabled observatory, focusing on the 2006 Kuril Island earthquake (Mw 8.3) as a far-field event and the 2008 off-Tokachi earthquake (Mw 6.8) as a near-field event. The Kuril Islands earthquake was detected as a series of tsunami signals by 2 bottom pressure gauges roughly 1 hour after the earthquake. Tsunami amplitudes observed offshore were 3 cm and off-coastal amplitudes were a few tens of centimeters. In the 2008 near-field off-Tokachi earthquake (Mw 6.8), a tsunami signal was detected simultaneously with the earthquake, which had a source amplitude of 4 cm. Our tsunami calculation reproduced the first wave well, but discrepancies about arrival time and amplitude arose for the second and later waves. Offshore tsunami sensors such as bottom pressure gauges, deep-ocean assessment and reporting of tsunami (DART) buoys, and kinematic global positioning system (GPS) buoys may thus become keys in early tsunami warning once appropriate dataset processing is implemented.